The small intestine transports large quantities of fluid daily, 8 liters, and this fluid must leave the intestinal interstitium by either the lymphatics or blood routes. Any changes in capillary forces, i.e., capillary pressure or plasma colloid osmotic pressure, that favor filtration into the intestinal interstitium will result in decreases in intestinal movement of solvent. We will measure the intestinal tissue forces, i.e., tissue pressure, tissue colloidal osmotic forces and lymph flow and relate these force changes to Alterations in intestinal absorption. These effects of cholera toxin, epinephrine, norepinephrine, acetylcholine and secretin on intestinal absorption will be studied in relation to the changes in the intestinal tissue and capillary forces. The results of these studies will allow a model of intestinal transport to be formulated that not only utilizes active transport systems, but one that also incorporates how the capillary and tissue force changes the net absorption.